The main software is what todesign said. For easy solutions you can even use illustrator or photoshop's latest veriions

Yea completely agree all depends on your drawing ability in photoshop and illustrator I've seen people create the same standard of imagery just in photoshop. God you can do everything in photoshop now a days. Especially now they've added al the 3d functions.

Photoshop + Illustrator is the norm for Pre-production mockups and displays.

Base white product with lighting is combined in Photoshop with 2D arrk from illustrator (which is sent for print/production), transforms and layer effects to produce a 3D representation of the product prior to production.

Doing this way ensures no errors/ommissions as the 2D file is the same for production and the mockup.

If money is an object you can also use Blender, which is free. Most 3D software is, at the core, similar. The exceptions being sculpting apps like Mudbox and ZBrush, and node-based weirdness like Houdini. Modo, 3ds, Softimage, Maya, Cinema4D, Lightwave, Silo, Blender, even Sketchup. etc... will all get you there. For protoyping you could use Autocad, Rhino, Alias, Solidworks, and so on. These last ones are more complicated, since they're more concerned with real-life parametric design than approximating geometry via (ultimately) triangles. All have some degree of learning curve making "best" a very relative term.
Once you've made your model you'll have to texture/surface and light and render it, and this can be as much of a task as making the model in the first place. Depending on what you're doing, it can make a very simple image non-trivial indeed.

Ive always used 3dsMax, but thats just because its what was on the machines at my first agency. Any of the big 3D software programs will be pretty similar. Just pick the one you like the interface of and start learning it!